Food

Volume 30 Number 1

Fall 2007

Photo courtesy Armin Moczek

Beetle-mania

When it comes to model organisms for biological research, the lowly beetle is making a big mark.

Beetles are diverse, numerous, and widespread. They represent the largest group of insects, accounting for a fifth of all living species and a fourth of all named animals. In fact, more beetle species exist on Earth than plants. Indiana University Bloomington biologist Armin Moczek is interested in all beetles, but he focuses on a kind of beetle most of us prefer to ignore--the dung beetle. Dung beetles happen to have particularly impressive horns, and Moczek recently received a second National Science Foundation grant of $538,000 for his research into the origin and diversification of beetle horns.

Why horns? We know many thousands of species of beetles use their horns as jousting weapons in combat over females. Moczek argues that the ornate, diverse, and often bizarre horns atop the heads of beetles can reveal much more about the processes of evolution and development, such as how new traits come into being and how and why those traits change over time.

In an earlier study, Moczek looked at why beetle horns evolved in the first place. Using species in which only large males have big horns, while females or small males are hornless, Moczek reared the beetles in the laboratory for several generations, observing that all the individuals--males, females, large and small--grew horns at early developmental stages. But the majority of the beetles in the lab reabsorbed their horns, turning into hornless adults. The only ones to retain their horns were large males. Moczek looked at additional species and found that this now-you-see-it-now-you-don't developmental pattern of horns was common. So, why did the hornless beetles grow horns to begin with?

When Moczek found a way to prevent beetle larvae and pupae from developing horns, it quickly became clear that larval and pupal horns were crucial tools for the correct molting of larval and pupal shells during metamorphosis. Without them, developing beetles remained stuck in their old shells, destined to die. "It turns out that simple pupal horns are very widespread, including beetles that never have horns in the adult stage," Moczek says. His findings suggest that pupal horns came first, helping juvenile beetles with molting and metamorphosis, and only secondarily became the weapon of choice among adult beetles.

To Moczek and other evolutionary biologists, understanding developmental processes such as the growth of beetle horns is crucial, because evolution doesn't build on structures (e.g., red feathers or long necks) so much as it builds on the developmental processes that create those structures. Development offers a window into what it takes for an organism to build itself, and what it takes for evolution to modify that process. "Evolution can only work with what it has, with what development will allow," Moczek says.

With the current NSF funding over the next three years, Moczek and his colleagues have three goals: to pin down genes that govern the formation of horns, figure out how programmed cell death (apoptosis) plays a role in horn shaping, and determine how key hormones and growth factors influence the size and location of horns.

Investigating the early stages in an individual's growth is key, Moczek says. "Even today, evolutionary theory is very much a theory of adults. But evolution doesn't morph one adult shape into another. There's an entire lifetime of development that we can't afford to ignore."